From the Account Settings menu, just under Pokes, tap on "Country".
You will then be presented with this screen:
When you register, EcchiDreams will usually guess which Country you're from. Sometimes it can't tell, and sometimes it might get it wrong. Sometimes, you might want to appear to be from a different country for whatever reason. You can correct or edit this by clicking on the drop down box to show the array of countries (which you can find in the introduction of this guide), and tap save. That's it.
If you don't want to view other Dreamer's Flags, then tap on the slider to disable it, and tap save. That's it.
This will then appear on your profile like so: